1. Field of the Invention
The present invention relates to a substrate processing apparatus and method for forming a film on the surface of an object to be processed.
2. Description of the Related Art
A predetermined circuit pattern is generally formed on the surface of an object such as a semiconductor wafer (to be referred to as a wafer hereinafter) using photolithography in a semiconductor device manufacturing process. The number of layers constituting a circuit pattern has been increased along with a recent increase in integration density of semiconductor elements. In such a multilayered wiring structure, it is important to reduce unevenness of a lower wiring layer. For this purpose, a technique for planarizing an insulating interlayer for insulating the upper and lower wiring layers has been examined.
A method using SOG (Spin On Glass) is known as a conventional method of planarizing an insulating interlayer. According to this SOG coating method, a process solution (SOG solution) obtained by mixing a silanol compound such as Si(OH).sub.4, i.e., a component serving as a film and a solvent such as ethyl alcohol is coated on a wafer serving as an object. The resultant structure is heat-treated to evaporate the solvent, and a polymerization reaction of the silanol compound progresses to form an insulating film. More specifically, first of all, a wafer is placed on a spin chuck. The SOG solution is dropped on the wafer while the wafer is rotated at a speed of 2,000 to 6,000 rpm, thereby forming an SOG film on the wafer. The SOG film is pre-heated at 100 to 140.degree. C. to evaporate the solvent. The resultant structure is further heat-treated at about 400.degree. C. to polymerize the silanol compound constituting the SOG film as siloxane bonds. To form a multilayered SOG film, the step of coating the SOG solution on a wafer and the step of evaporating the solvent are repeated, and then a heat treatment is performed. Alternatively, the step of coating the SOG solution on a wafer, the step of evaporating the solvent, and a heat treatment are repeatedly performed.
In the step of coating the SOG solution on the surface of the wafer, the SOG solution is dropped on the surface of the wafer during rotation of the wafer, thereby coating the SOG solution on each wafer according to the spin-coating method (single wafer process). On the other hand, in consideration of working efficiency, a batch process in which a plurality of wafers are preferably held by a holding means such as a wafer boat, loaded in a heating apparatus, and heat-treated is suitable in the step of heat-treating wafers upon application of the SOG solution. For this reason, the coating step in the single wafer process and the heat-treatment step in batch process are conventionally performed in separate apparatuses.
When the coating step and the heat-treatment step are performed by the separate apparatuses, a large space is required, and the total apparatus size becomes undesirably large. The processing efficiency is also degraded because an object is loaded in a heat-treatment apparatus once it is conveyed outside the coating apparatus upon completion of the coating step. An organic material, fine dust, and the like are attached to the coated surface because the object is exposed to the outer air upon the coating step. The organic material, fine dust, and the like become particles to cause a decrease in product yield. To solve these problems, greatest care must be taken for management of objects which have undergone the coating process.